There is a smart host that needs RS-485 communication with several RS-232 devices. Some people say that it needs a star connection, and some say it can also be connected in parallel. Some people say that it is hand-in-hand communication. Which communication is correct?
This depends on 3 points: 1, distance, 2, location distribution, 3, number of nodes.
The distance between the scenes is very close, and the distribution has straight lines, stars, and rings, and the number of nodes is more or less. The simplest is direct parallel, but the distance and nodes are limited. As for the star and the ring, it depends entirely on the local distribution of each device node.
This paper introduces and compares the hand-in-hand solution with the direct parallel solution, indicating that the hand-in-hand can achieve the connection of unlimited distance and number of nodes.
1, simple RS-485 direct parallel connection
This direct parallel connection is also the easiest way to connect RS-485. Five RS232 devices are equipped with five 485A converters, and then the RS-485 terminals are directly connected in parallel (all A are connected together and all Bs are connected together). The distance is limited by a distance of up to 1200 meters and the limit of 128 nodes. In most cases it is possible to communicate.
2, hand-in-hand RS-485 connection
It seems to be similar to direct parallel, but please note that each 485A2 converter has 2 RS-485 ports. In the figure, you can see that the two RS-485s of each 485A2 converter are equivalent to two hands, and the connection method looks like hand-in-hand. The 485A2 converter also becomes an RS-232/RS-485 relay converter. Its two RS-485s have mutual relay functions, so the communication distance is extended by 1200 meters and the number of communication nodes is increased by one 485A2. Also add 128 more. In this way, it is more convenient to use without worrying about how many nodes have been laid and how far away they are. Note that the farthest ends can use 485A because only one RS485 port is used.
If there is a more extreme situation, the distance of each segment is required to exceed 1200 meters, then the RS485 fiber optic relay converter OPT35EXS can be used, which is also a hand-in-hand connection, but the wires are replaced by optical fibers.
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